Light emitting device with small footprint

ABSTRACT

This application describes a light emitting device or an assembly of light emitting devices, each with a small footprint. The light emitting device comprises two transistors, a capacitor, and an LED. The transistors comprise single crystal semiconductor. The capacitor is vertically-oriented. The LED overlies the transistors and capacitor. Methods to form the light emitting device or assembly are discussed.

RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.16/835,614 filed Mar. 31, 2020, which is assigned to the assignee hereofand filed by the inventor hereof and which is incorporated by referenceherein.

FIELD

The embodiments of the invention are directed generally to lightemitting devices having a small footprint. The light emitting devicecomprises two transistors, a capacitor, and a light emitting diode(LED). The light emitting device with small footprint may be used as asubpixel in a display, or present as a single point light source.

BACKGROUND

Displays may comprise assemblies of pixels. A pixel may comprise threesubpixels, each subpixel emitting light of a different dominantwavelength. A subpixel is a light emitting device. The dominant lightwavelength emitted by the subpixel corresponds to a color. For example,a pixel may comprise three subpixels emitting red, green, and bluelight, respectively. In this case, the pixel can emit light of any colorby turning on or off its various subpixels. By controlling theindividual brightness of three subpixels emitting red, green, and bluelight, the combined light output of these three subpixels may be anycolor such as pink or cyan. Pixels capable of multicolor light emissionmay form a color display. A two dimensional array of pixels is a commonarrangement for a display. Monochrome displays comprise pixels that emitonly one wavelength of light. In the case of monochrome displays, apixel may comprise only one light emitting device, and so for amonochrome display only, a pixel and subpixel may be the same thing. Thesubpixel apparatus may be used as part of a color display or amonochrome display, or any other suitable application, for example,single point light sources.

A light emitting device may comprise a light source, such as an LED, anda control apparatus to switch the LED on and off. In a commonarrangement for active matrix displays, the control apparatus of a lightemitting device may comprise two transistors and a capacitor. The drivetransistor controls the brightness of the light emitting device. Theaddress transistor receives a scanning signal to its gate, and the drainof the address transistor is connected to a data line to receive animage data signal. A source terminal is connected to the gate of thedrive transistor to control the on/off states of the drive transistor.The source or drain of the drive transistor is connected to an electrodeof the LED. The capacitor is connected to the gate of the drivetransistor and assists the drive transistor to stay in an on or offstate.

When each subpixel in a display is selectively addressed by itsindividual transistor(s) to change the state of the subpixel, thearrangement is known as an active matrix display. The resolution of adisplay may be improved by using subpixels with smaller area and/orpacking them more closely together. This technique can also be used toshrink the size of a display. Small displays, such as those for watchesor augmented reality headsets, require small subpixels. Small subpixelsrequire small LEDs. In a conventional subpixel apparatus, the controldevices are placed alongside the LED, with the area of the subpixelbeing the areas of the control apparatus and the LED, and otherassociated elements such as interconnects and unoccupied space such asneeded for insulating one subpixel from a neighboring subpixel and formanufacturing tolerance. Conventional subpixels also utilize thin filmtransistors, where the transistor channel comprises a polycrystalline oramorphous semiconductor material with low carrier mobility.

SUMMARY

Embodiments described herein provide for a light emitting device with asmall footprint or an assembly of light emitting devices, and methods offabrication of same. A specific embodiment is for a light emittingdevice with a transistor substrate having a top surface and bottomsurface, wherein the top surface comprises a plurality of conductiveregions. There is a plurality of through substrate interconnects in thelight emitting device, wherein each through substrate interconnectextends from one of the conductive regions to the bottom surface of thetransistor substrate. First and second transistors are formed in the topsurface of the transistor substrate. A capacitor has its longestdimension substantially orthogonal to the top surface of the transistorsubstrate and is in operative communication with the first and secondtransistors. An LED having a largest area overlies the first and secondtransistors and capacitor. The LED is in operative communication witheither the first or the second transistor. The LED comprises galliumnitride, indium gallium nitride, indium arsenide, aluminum galliumarsenide, gallium arsenide, gallium phosphide, gallium arsenidephosphide, aluminum indium gallium phosphide, gallium arsenide nitride,aluminum indium arsenide, aluminum antimonide, indium phosphide, indiumantimonide, or indium gallium arsenide phosphide, and combinationsthereof.

In another embodiment, an assembly of light emitting devices comprises atransistor substrate having a top surface and a bottom surface, whereinthe top surface comprises a plurality of conductive regions. Theassembly has a plurality of light emitting devices. Each light emittingdevice comprises a plurality of through substrate interconnects. Eachthrough substrate interconnect extends through the transistor substratefrom one of the conductive regions to the bottom surface of thetransistor substrate. Each light emitting device comprises a firsttransistor and a second transistor, both formed in the top surface ofthe transistor substrate. Each light emitting device comprises acapacitor, wherein the longest dimension of the capacitor issubstantially orthogonal to the top surface of the transistor substrate,and wherein the capacitor is in operative communication with the firsttransistor and the second transistor. Each light emitting devicecomprises an LED having a largest area and wherein the LED overlies thefirst and second transistors and the LED. The assembly comprises aplurality of wavelength-converting layers, wherein at least onewavelength-converting layer emits light with a dominant wavelength ofbetween 500 and 550 nm and second wavelength-converting layer emitslight with a dominant wavelength of between 610 and 730 nm. The assemblycomprises a backboard wherein the backboard comprises a plurality ofbackboard interconnects.

In another embodiment, a method to fabricate a light emitting devicecomprises the steps of providing a transistor substrate, the transistorsubstrate having a top surface and a bottom surface. The top surface ofthe transistor substrate has a plurality of conductive regions. Twotransistors are formed in the top surface of the transistor substrate. Acapacitor is formed. An LED is formed on an LED substrate, and the LEDhas a largest area. The LED comprises gallium nitride, indium galliumnitride, indium arsenide, aluminum gallium arsenide, gallium arsenide,gallium phosphide, gallium arsenide phosphide, aluminum indium galliumphosphide, gallium arsenide nitride, aluminum indium arsenide, aluminumantimonide, indium phosphide, indium antimonide, or indium galliumarsenide phosphide, and combinations thereof. A reflector layer isformed. The two transistors, capacitor, and transistor substrate arebonded to the LED. After bonding, the reflector layer is disposedbetween the LED and transistor substrate, the LED is in operativecommunication with at least one of the two transistors, and the LEDoverlies the transistors and capacitor. A portion of the originaltransistor substrate is then removed, and a plurality of throughsubstrate interconnects are formed in the remaining transistorsubstrate. Each through substrate interconnect extends from a conductiveregion to the bottom surface of the transistor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are idealized representations to describe embodiments ofthe present disclosure and are not meant to be actual views of anyparticular component, structure, or device. The drawings are not toscale, and the thickness and dimensions of some layers may beexaggerated for clarity. Variations from the shapes of the illustrationsare to be expected. For example, a region illustrated as a box shape maytypically have rough and/or nonlinear features. Sharp angles that areillustrated may be rounded. Like numerals refer to like componentsthroughout. The features, aspects, and advantages of the embodimentsdescribed herein will become better understood with regard to thefollowing description, appended claims, and accompanying drawings,where:

FIG. 1 schematically illustrates an example of a cross-sectional view ofone element overlying a second element as seen by a viewer.

FIG. 2 schematically illustrates an example of a cross-sectional view ofone element overlying a second element as seen by a viewer.

FIG. 3 schematically illustrates an example of a cross-sectional view ofone element overlying a second element as seen by a viewer.

FIG. 4 schematically illustrates an example of a cross-sectional view oftwo elements as seen by a viewer.

FIG. 5 schematically illustrates a cross-sectional view of oneembodiment of a light emitting device with two single crystaltransistors and a stack capacitor underlying an LED with one LEDvertical interconnect.

FIG. 6 schematically illustrates a cross-sectional view of oneembodiment of a light emitting device with two single crystaltransistors and a stack capacitor underlying an LED with two LEDvertical interconnects.

FIG. 7 schematically illustrates a cross-sectional view of oneembodiment of a light emitting device with two single crystaltransistors and a trench capacitor underlying an LED with one LEDvertical interconnect.

FIG. 8 schematically illustrates a cross-sectional view of oneembodiment of a light emitting device with two single crystaltransistors and a trench capacitor underlying an LED with two LEDvertical interconnects.

FIG. 9A schematically illustrates a cross-sectional view of an LED on anLED substrate.

FIG. 9B schematically illustrates a plan view of the LED shown in FIG.9A.

FIG. 9C schematically illustrates a plan view of another example of anLED.

FIG. 10A schematically illustrates a cross-sectional view of an LED onan LED substrate.

FIG. 10B schematically illustrates a plan view of the LED shown in FIG.10A.

FIG. 10C schematically illustrates a plan view of another example of anLED.

FIG. 11A schematically illustrates a cross-sectional view of an LED witha reflector layer.

FIG. 11B schematically illustrates a cross-sectional view of an LED witha reflector layer and a single LED vertical interconnect.

FIG. 11C schematically illustrates a cross-sectional view of an LEDapparatus with an LED, a reflector layer, a single LED verticalinterconnect, and a bond pad layer.

FIG. 12 schematically illustrates a cross-sectional view of an LEDapparatus with an LED, a reflector layer, two LED verticalinterconnects, and a bond pad layer.

FIG. 13A schematically illustrates a cross-sectional view of transistorsand a transistor substrate.

FIG. 13B schematically illustrates a cross-sectional view oftransistors, a transistor substrate, and transistor verticalinterconnects.

FIG. 13C schematically illustrates a cross-sectional view oftransistors, a transistor substrate, transistor interconnects, and alower stack capacitor electrode layer.

FIG. 13D schematically illustrates a cross-sectional view oftransistors, a transistor substrate, transistor interconnects, and alower stack capacitor electrode layer.

FIG. 13E schematically illustrates a cross-sectional view of a controlapparatus.

FIG. 14A schematically illustrates a cross-sectional view of the lowertrench capacitor electrode in a transistor substrate.

FIG. 14B schematically illustrates a cross-sectional view of the lowertrench capacitor electrode with a mold nitride layer.

FIG. 14C schematically illustrates a cross-sectional view of the lowertrench capacitor electrode with a mold nitride layer and transistorsformed in the upper surface of the transistor substrate.

FIG. 14D schematically illustrates a cross-sectional view of a trenchcapacitor and transistors.

FIG. 14E schematically illustrates a cross-sectional view of a controlapparatus.

FIG. 15A schematically illustrates a cross-sectional view of the actionof flipping an LED apparatus and bonding to a control apparatus.

FIG. 15B schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus.

FIG. 16A schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus with both substrates intact.

FIG. 16B schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus after a portion of thetransistor substrate has been removed.

FIG. 16C schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus after formation of throughsubstrate interconnects.

FIG. 16D schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus after formation of a bond padlayer on the bottom surface of the transistor substrate.

FIG. 17 schematically illustrates a cross-sectional view of the bondedpair of LED apparatus+control apparatus after bonding to a backboard.

FIG. 18A schematically illustrates a cross-sectional view of thepartially fabricated light emitting device after roughening the surfaceof the lower conductive layer of the LED.

FIG. 18B schematically illustrates a cross-sectional view of thepartially fabricated light emitting device after deposition of atransparent conductive layer and a wavelength-converting layer.

FIG. 19A schematically illustrates a cross-sectional view the action offlipping a wavelength-converting layer comprising a MQW layer withsubstrate and bonding to the transparent conductive layer of an LED.

FIG. 19B schematically illustrates a cross-sectional view of the LEDapparatus+control apparatus+MQW layer, after removal of MQW substrate.

FIG. 19C schematically illustrates a cross-sectional view of partiallyfabricated light emitting device with a dielectric layer in between thewavelength-converting layer and LED.

FIG. 20A schematically illustrates a cross-sectional view of anembodiment of an assembly of light emitting devices.

FIG. 20B schematically illustrates a cross-sectional view of anembodiment of an assembly of light emitting devices.

DETAILED DESCRIPTION OF EMBODIMENTS

It is desirable to reduce the area of the LED in a light emitting deviceto enable higher resolution in a display and/or a smaller display. Forthe embodiments in this application, the LEDs will be inorganicsemiconductors, and not organic semiconductors. For example, inconventional devices, multiple larger area LEDs may be fabricated on asubstrate with an area of over 1000 millimeters squared and thenseparated into single large-area LED dies measuring 200 microns×200microns. The large-area LED dies may include a portion of the LEDsubstrate. These large area LED dies may then be mechanically placedinto a package with other LED dies, and wire bonded to connect the LEDsto other devices, for example, control devices comprising thin filmtransistors that are alongside the LED.

Small area LEDs have sometimes been called micro-LEDs. Micro-LEDs mayhave lateral dimensions of 50 microns×50 microns, 50 microns×20 microns,20 microns×20 microns, 10 microns×10 microns, or even smaller. Thelargest area of a square-shaped LED with dimensions 50 microns×50microns is 2500 microns squared. The largest area of a square-shaped LEDwith dimensions 10 microns×10 microns is 100 microns squared. In thisapplication, micro-LEDs will have a largest area of 2500 microns squaredor less. Fabrication of displays using micro-LEDs requires differenttechniques compared to the fabrication of larger area LEDs. As the LEDarea shrinks to micro-LED size of 50 microns×50 microns or less,mechanical placement and wire bonding of individual micro LEDs is nolonger feasible. New techniques must be employed to assemble micro-LEDsinto displays. To decrease the area of the light emitting device and thedisplay, it is advantageous to fit the control apparatus underneath theLED. In embodiments described herein, the control devices fit underneaththe LED in the completed light emitting devices. When viewed top-down,the LED will at least partially obscure the control apparatusunderneath, and more preferably completely obscures it. To enable theLED to have a small area and yet still fit the control devicesunderneath, the control apparatus is fabricated in a manner to occupy asmall footprint.

Control devices comprising conventional horizontal thin film transistorsand horizontal capacitors have a large footprint. Thin film transistors,with polycrystalline or amorphous channels, have lower carrier mobilitycompared with single crystal transistors, where the channel is singlecrystal material. For approximately equivalent dimensions and operatingvoltages, a single crystal transistor will provide a higher current thana thin film transistor due to its higher carrier mobility. In general, asingle crystal transistor can provide the same saturation current as athin film transistor that is many times the size of the single crystaltransistor. Some embodiments of the present invention describe a lightemitting device with a control apparatus comprising single crystaltransistors and vertically-oriented capacitors. LEDs are usuallysubstantially planar devices, having a first surface opposite a secondsurface. The first and second surfaces are substantially planar andparallel to one another and are separated by a thickness. For example, asubstantially planar micro-LED may have first and second polygonsurfaces that are square shapes with dimensions of 20 microns×20 micronsand a thickness of 2 microns. The largest area of the LED in thisexample would be 400 microns squared. In conventional displays, asubstantially planar LED in a subpixel apparatus may have dimensions of,for example, 200 microns×200 microns, resulting in a largest area of40,000 microns squared.

Embodiments of the present invention will employ vertically-orientedcapacitors that have the longest dimension substantially orthogonal tothe planar transistor substrate, minimizing the footprint of thecapacitor. In contrast, horizontally-oriented capacitors have theirlongest dimension parallel to the transistor substrate. The embodimentsof the present invention have single crystal transistors withinterconnects extending through the single crystal transistor substrate.Another benefit to fitting the control devices underneath thesubstantially planar LED is the reduction in resistance losses thatcomes with short interconnection between the LED and the control devicesthat is a result of stacking the LED over the control devices.

Fabrication methods for inorganic LEDs and their control devices aredifferent than for organic LEDs and their control devices. InorganicLEDs comprising materials such as but not limited to gallium nitride,indium gallium nitride, indium arsenide, aluminum gallium arsenide,gallium arsenide, gallium phosphide, gallium arsenide phosphide,aluminum indium gallium phosphide, gallium arsenide nitride, aluminumindium arsenide, aluminum antimonide, indium phosphide, indiumantimonide, or indium gallium arsenide phosphide, and combinationsthereof are fabricated on single crystal LED substrates. These singlecrystal LED substrates serve as a template or seed, so that the LEDfabricated upon them is substantially single crystal as well. Singlecrystal LED substrates, for example, silicon, sapphire, or siliconcarbide, are typically more than 400 microns thick during LEDfabrication, to enable a large surface that is mechanically robust onwhich to economically fabricate many thousands of LEDs simultaneously.Inorganic single crystal LED fabrication occurs at high temperatures,typically over 850° C., and often over 1000° C., for a duration lasting30 minutes or more. The control apparatus for the LEDs includestransistors. Exposing transistors to thermal cycles in excess of 850° C.for 30 minutes or longer will degrade or even ruin the desiredelectrical properties of many types of transistors. Therefore,fabricating inorganic LEDs on substrates comprising transistors is notpractical. Light emitting devices with inorganic LEDs are made byforming the LEDs on an LED substrate at high temperatures, forming thecontrol apparatus on a separate transistor substrate, and then combiningthe LED and control apparatus. In this manner the control apparatus isnot exposed to the high temperatures necessary for inorganic LEDfabrication. In contrast, organic LEDs, comprising such materials aspoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), commonly knownas PEDOT:PSS, are typically fabricated at temperatures of 200° C. orless. Temperatures of 200° C. or less have relatively little effect onthe electrical properties many types of transistors. Therefore, it ispractical to fabricate organic LEDs on substrates with transistors andavoiding a separate combining step.

As used herein, the term “overlying” describes a second element that atleast partially obscures a first element or elements when the secondelement is between the first element or elements and a viewer. The term“underlying” describes a first element or elements that is or are atleast partially obscured by a second element when the second element isbetween a viewer and the first element or elements. The viewer is on aline orthogonal to the center of the surface of the second elementfacing the viewer of the second element. As shown by example in FIG. 1,a second element 2 overlies a first element 1 because second element 2lies between first element 1 and a viewer 3, and second element 2obscures first element 1 from viewer 3. In FIGS. 1-3, the dimension L2is the distance between viewer 3 and second element 2, and the dimensionL1 is the distance between element 1 and element 2. The ratio of L2 toL1 is at least 100×. In one example, dimension L2 is 2 meters anddimension L1 is 2 microns, and the ratio L2/L1 is 1,000,000×. In FIGS.1-4, the surface 5 is the surface of the second element facing viewer 3,and line 4 is orthogonal to the surface 5 and transits the center ofsurface 5. First element 1 underlies second element 2 in FIG. 1. Firstelement 1 is completely obscured from viewer 3 by second element 2 inFIG. 1. In another example shown in FIG. 2, a second element 2 overliesa first element 1 because second element 2 lies between first element 1and viewer 3, and second element 2 obscures first element 1 from viewer3. First element 1 underlies second element 2. In this example, thefirst element 1 is partially obscured by second element 2 from viewer 3,with portion 1A of first element 1 that does not underlie second element2. In another example shown in FIG. 3, a second element 2 overlies afirst element 1 because second element 2 lies between first element 1and a viewer 3 and second element 2 obscures first element 1 from viewer3. First element 1 underlies second element 2. In this example, thefirst element 1 is partially obscured by second element 2 from viewer 3,with portion 1A of first element 1 that does not underlie second element2. In another example shown in FIG. 4, a second element 2 does notoverlie a first element 1 because second element 2 does not obscurefirst element 1 from a viewer 3.

When an element is referred to being “directly on” on another element,there are no intervening elements present. As used herein, the phrase“operative communication” describes a functional connection. As usedherein, the phrase “largest area” refers to the largest area or largestareas of multiple areas that enclose a solid element. There may be morethan one largest area. For example, a box enclosed by squares of equallength sides will have six largest areas, all equal in size. As usedherein, the phrase “longest dimension” refers to the largest dimensionof an object, wherein the object has a size defined by its threedimensions in the X-Y-Z Cartesian coordinate system. The largestdimension will be substantially parallel to one of the X, Y, or Z axes.Particular features described herein can be used in combination withother described features in each of the variously possible combinationsand permutations.

In this application, some embodiments of a light emitting device or anassembly of light emitting devices are described. In a first embodiment,a light emitting device is described comprising two single crystaltransistors and a stack capacitor underlying a substantially planar LEDwith one LED vertical interconnect. In a second embodiment, a lightemitting device is described comprising two single crystal transistorsand a stack capacitor underlying a substantially planar LED with two LEDvertical. In a third embodiment, a light emitting device is describedcomprising two single crystal transistors and a trench capacitorunderlying a substantially planar LED with one LED verticalinterconnect. In a fourth embodiment, a light emitting device isdescribed comprising two single crystal transistors and a trenchcapacitor underlying a substantially planar LED with two LED verticalinterconnects. Other embodiments further comprising reflector layersand/or wavelength converting layers are described. Examples of methodsto fabricate a light emitting device are described, along with thefunction of the elements. Finally, some embodiments of assemblies oflight emitting devices will be described.

Turning to FIG. 5, an embodiment of a light emitting device is shown incross-sectional view. The light emitting device comprises a transistorsubstrate 100 having a top surface 102 and a bottom surface 106. Topsurface 102 and bottom surface 106 are planes that extend through thepage. Top surface 102 comprises a plurality of conductive regions 120.Conductive regions 120 are shown as areas but are in reality volumesthat extend through the page like all of the elements of the lightemitting device when shown in cross-section. The light emitting devicecomprises a first transistor 200 and second transistor 300, both ofwhich are formed in transistor substrate 100. The light emitting devicealso comprises a capacitor 400S. Capacitor 400S is a stack capacitorhaving a longest dimension C1. In other embodiments (not shown),capacitor 400S may be a planar capacitor. Dimension C1 is substantiallyorthogonal to top surface 102 of transistor substrate 100. The lightemitting device also comprises an LED 500 that is substantially planar.LED 500 has dimension LD1 and another dimension extending orthogonallythrough the page (not shown) that defines the largest area of LED 500.The largest area of LED 500 overlies first transistor 200, secondtransistor 300, and capacitor 400S. The thickness of LED 500 as well asthe roughness of one of its surfaces has been exaggerated for clarity.LED 500 comprises gallium nitride, indium gallium nitride, indiumarsenide, aluminum gallium arsenide, gallium arsenide, galliumphosphide, gallium arsenide phosphide, aluminum indium galliumphosphide, gallium arsenide nitride, aluminum indium arsenide, aluminumantimonide, indium phosphide, indium antimonide, or indium galliumarsenide phosphide, and combinations thereof. A plurality of throughsubstrate interconnects 140 extend from conductive regions 120 to thebottom surface 106 of transistor substrate 100. A single LED verticalinterconnect 506 is in contact with LED 500. A transparent conductivelayer 576 is also in contact with LED 500. In this embodiment, capacitor400S is a stack capacitor and is disposed between second transistor 300and LED 500. Capacitor 400S is in operative communication with firsttransistor 200 and second transistor 300 through transistor verticalinterconnects 242 a, 242 b, and 240 b. LED 500 is in operativecommunication with second transistor 300 through LED verticalinterconnect 506 and transistor vertical interconnect 410. A reflectivelayer 550 is disposed between LED 500 and transistor substrate 100. Awavelength-converting layer 578 overlies LED 500. The areas betweentransistors 200 and 300, capacitor 400S, and between these devices andLED 500 which are not occupied by interconnects, reflector layers, orwavelength-converting layers are occupied with dielectric material, forexample, silicon oxide (not shown). Other embodiments of this device maynot have a reflective layer 550 or wavelength-converting layer 578.

Turning to FIG. 6, a different embodiment of a light emitting device isshown in cross-sectional view. The light emitting devices comprises mostof the same elements shown in FIG. 5, except LED 500 has two LEDvertical interconnects 506 and 508 contacting it. There will be a moredetailed discussion of LED fabrication, including plan views, in a latersection.

Turning to FIG. 7, a different embodiment of the present invention isshown in cross-sectional view. The light emitting device comprises atransistor substrate 100 having a top surface 102 and a bottom surface106. Top surface 102 comprises a plurality of conductive regions 120.The light emitting device comprises a first transistor 200 and secondtransistor 300, both of which are formed in transistor substrate 100.The light emitting device also comprises a capacitor 400T. Capacitor400T is a trench capacitor having a longest dimension C2, and at least aportion of capacitor 400T is disposed between top surface 102 and bottomsurface 106 of transistor substrate 100. In other embodiments (notshown), capacitor 400T may be a planar capacitor. Dimension C2 isorthogonal to top surface 102 of transistor substrate 100. The lightemitting device also comprises an LED 500 that is substantially planar,and has a largest area overlying first transistor 200, second transistor300, and capacitor 400T. LED 500 comprises gallium nitride, indiumgallium nitride, indium arsenide, aluminum gallium arsenide, galliumarsenide, gallium phosphide, gallium arsenide phosphide, aluminum indiumgallium phosphide, gallium arsenide nitride, aluminum indium arsenide,aluminum antimonide, indium phosphide, indium antimonide, or indiumgallium arsenide phosphide, and combinations thereof. A plurality ofthrough substrate interconnects 140 extend from conductive regions 120to the bottom surface 106 of transistor substrate 100. A single LEDvertical interconnect 506 is in contact with LED 500. A transparentconductive layer 576 is also in contact with LED 500. Capacitor 400T isin operative communication with first transistor 200 and secondtransistor 300, through transistor vertical interconnects 242 a and 240b, horizontal interconnect 374 b, and conductive region 120. LED 500 isin operative communication with second transistor 300 through LEDvertical interconnect 506 and transistor vertical interconnect 410. Areflective layer 550 is disposed between LED 500 and transistorsubstrate 100. A wavelength-converting layer 578 overlies LED 500. Theareas between transistors 200 and 300, capacitor 400T, and between thesedevices and LED 500 which are not occupied by interconnects, reflectorlayers, or wavelength-converting layers are occupied with dielectricmaterial, for example, silicon oxide, not shown. Other embodiments ofthis device may not have a reflective layer 550 or wavelength-convertinglayer 578.

Turning to FIG. 8, a different embodiment of a light emitting device isshown in cross-sectional view. The light emitting device comprises mostof the same elements shown in FIG. 7, except LED 500 has two LEDvertical interconnects 506 and 508 contacting it.

I. Single Light Emitting Device Fabrication

Some embodiments of the fabrication of a single light emitting deviceand the function of its elements will be discussed in section I. The LEDand fabrication will be described in subsection IA. LED fabrication willoccur on an LED substrate, although the LED substrate will be removed ina subsequent step. The LED, LED substrate, and associated elements suchas passivating dielectric layers, LED vertical interconnects, and a bondpad layer will collectively be called the LED apparatus. The transistorsand their fabrication will be described in subsection IB. The stackcapacitor and its fabrication will be described in subsection IC. Thetrench capacitor and its fabrication will be described in subsection ID.The transistors and capacitor will be fabricated on a transistorsubstrate. The transistors, capacitor, transistor substrate, andassociated elements such as passivating dielectric layers and transistorvertical interconnects, and a bond pad layer will collectively be calledthe control apparatus. A bonding process will join the control apparatuswith the LED apparatus, as described in subsection IE Next, throughsubstrate interconnects extending from conductive regions of thetransistor substrate and fabrication methods will be described insubsection IF. The bonding of the combined LED apparatus, controlapparatus, and through substrate interconnects to a backboard will bedescribed in subsection IG. Finally, the formation ofwavelength-converting layers will be described in section IH Someembodiments of an assembly of light emitting devices comprising multiplelight emitting devices will be discussed in section II.

Some examples of methods to fabricate embodiments according to thepresent invention will be discussed. When reference is made herein to amethod comprising two or more defined steps, the defined steps can becarried out in any order or simultaneously (except where context orspecific instruction excludes that possibility), and the method caninclude one or more other steps carried out before any of the definedsteps, between two of the defined steps, and/or after all the definedsteps (except where context excludes that possibility). The fabricationprocesses described herein do not form a complete process flow, with theremainder of the process flow known to those of ordinary skill in theart. Only the methods and structures necessary to understand embodimentsof the present invention are described herein.

IA. LED Apparatus

One embodiment of the LED apparatus and fabrication is now described. Itis to be understood that fabrication of many LED apparatus is occurringsimultaneously on the same LED substrate although only one is shown.Turning to FIG. 9A, an LED 500 is formed on an LED substrate 510. LED500 comprises a first conductive layer 514 which is disposed on thesurface 512 of LED substrate 510, an active layer 516 disposed on firstconductive layer 514, and a second conductive layer 518 disposed onactive layer 516. Surface 512 is one surface of LED substrate 510, whichhas another substantially parallel surface 522. In this embodiment, anLED contact 530 is disposed on a portion of second conductive layer 518.In this embodiment, each of layers 514, 512, and 518 is in immediatecontact with the layer below it, with no intervening layers.

First conductive layer 514 and second conductive layer 518 may be anysuitable semiconductor layer known to those skilled in the art,including but not limited to gallium nitride, indium gallium nitride,indium arsenide, aluminum gallium arsenide, gallium arsenide, galliumphosphide, gallium arsenide phosphide, aluminum indium galliumphosphide, gallium arsenide nitride, aluminum indium arsenide, aluminumantimonide, indium phosphide, indium antimonide, or indium galliumarsenide phosphide. The first and second conductive layers 514 and 518may be gallium nitride doped to opposite polarity of one another, forexample, n-type and p-type or vice versa. Active layer 516 may befabricated of any standard semiconductor materials, for example indiumgallium nitride, in any formation, for example single quantum well,multiple quantum wells, or double heterostructure. In other embodiments,there may be so-called current blocking layers (not shown) above and/orbelow active layer 516 (i.e. the active layer 516 may be deposited on acurrent blocking layer, and a current blocking layer may be deposited onactive layer 516). The principles and mechanisms of the conductive andactive layers are well known to those skilled in the art. Any suitablemethod may be used to deposit LED semiconducting materials, includingbut not limited to metal organic chemical vapor deposition (MOCVD),hydride vapor phase epitaxy, molecular beam epitaxy, most preferablyMOCVD.

LED substrate 510 upon which LED 500 is fabricated is any suitablesingle crystal semiconductor, although any suitable substrate materialmay be used, including but not limited to sapphire, silicon carbide,gallium nitride, zinc oxide, and silicon. LED substrate 510 comprisessingle crystal material which is substantially crystal lattice matchedwith the first conductive layer 514. Substantially crystal latticematched is to mean the mismatch between the two crystal lattices is lessthan about 25%. For example, gallium nitride and sapphire aresubstantially crystal lattice matched, with a lattice mismatch of 16%.

LED contact 530 may be any suitable material to make an ohmic contact toconductive layer 518, including but not limited to indium tin oxide(ITO), aluminum zinc oxide (AZO), fluorine-doped tin oxide (FTO),aluminum, silver, nickel, or a stack of a nickel layer followed by agold layer. LED contact 530 may be deposited by any suitable technique,such as evaporation, CVD, or sputtering, most preferably evaporation.LED contact 530 may have been formed by etching a larger layer with amasking layer disposed on it (not shown), or by a lift-off technique.The masking layer is removed (not shown).

FIGS. 9B and 9C are schematic plan view illustrations of someembodiments of LEDs. FIG. 9B is a plan view of LED 500 with crosssection X-X′ in FIG. 9A. LED 500 in FIG. 9A has LED contact 530 near oneof the middle edges of conductive layer 518. An example of a differentplacement of the LED contact is shown in FIG. 9C. FIG. 9C is a plan viewschematic of a different LED, with LED contact 530 in one corner ofconductive layer 518. While LED contact 530 is shown in FIGS. 9B and 9Cas round, it may have any suitable shape, for example round with currentspreading lines emanating from the round shape. In one example, LEDcontact 530 may have a diameter of 1 micron in plan view, although anysuitable size may be used. While FIGS. 9B and 9C both show square-shapedLEDs in plan view, the LEDs may take any suitable shape in plan view,such as rectangular, triangular, or any other polygon. In the presentinvention, dimensions A1 and A2 in FIGS. 9A and 9B may be 50 microns, 10microns, 5 microns, or even smaller values. The largest area of LED 500is the largest area, i.e. the top or bottom, of the first conductivelayer 514. As shown in FIGS. 9A-C, the first conductive layer 514 is asquare shape with a thickness T1, thickness T1 being much smaller thandimensions A1 or A2. The thickness T1 is exaggerated in FIG. 9A forclarity. The surface area of the LED 500 is dimension A1 multiplied bydimension A2. In this embodiment, dimensions A1 and A2 are the same forfirst conductive layer 514 and second conductive layer 518. Theresulting largest area of LED 500 may be 2,500 square microns, 1,000square microns, 100 square microns, or even smaller values. The presentinvention is directed towards LEDs with largest areas less than or equalto 2,500 square microns. In another example, the dimensions A1 and A2are 10 microns, resulting in an LED largest area of 100 square microns.

Turning to FIG. 10A, an alternative embodiment for LED fabrication isillustrated. Referring to FIG. 10A, LED 500 is formed on LED substrate510 and is shown schematically in cross section. LED 500 comprises afirst conductive layer 514 which is disposed on the surface 512 of LEDsubstrate 510, an active layer 516 disposed on first conductive layer514, and a second conductive layer 518 disposed on active layer 516. Inthis embodiment, an LED contact 530 a is disposed on a portion of secondconductive layer 518, and another LED contact 530 b is disposed on aportion of first conductive layer 514. It is to be understood that thiscan represent one of many LEDs on LED substrate 510.

FIGS. 10B and 10C are schematic plan view illustrations of someembodiments of LEDs. FIG. 10B is a plan view of LED 500 with crosssection X″-X′″ in FIG. 10A. LED 500 has LED contacts 530 a and 530 bnear one of the middle edges of conductive layer 518 and conductivelayer 514, respectively. An example of a different placement of the LEDcontact is shown in FIG. 10C. FIG. 10C is a plan view schematic of adifferent LED, with LED contact 530 a in one corner of conductive layer518. While LED contact 530 is shown in FIGS. 10B and 10C as round, itmay have any suitable shape, for example round with current spreadinglines emanating from the round shape. In one example, LED contact 530may have a diameter of 1 micron in plan view, although any suitable sizemay be used. While FIGS. 10B and 10C both show square-shaped LEDs inplan view, the LEDs may take any suitable shape in plan view, such asrectangular, triangular, or any other polygon. In the present invention,dimensions A1 and A2 in FIGS. 10A and 10B may be 200 microns, 10microns, 5 microns, or even smaller values. The largest area of LED 500is the largest area, i.e. either the top or the bottom, of the firstconductive layer 514. The surface area of the LED 500 is dimension A1multiplied by dimension A2. In this embodiment, first conductive layer514 has a largest area that is larger than that of second conductivelayer 518. The resulting largest area of LED 500 may be 2,500 squaremicrons, 1,000 square microns, 100 square microns, or even smallervalues. The present invention is directed towards LEDs with smalllargest areas less than or equal to 2,500 square microns. In anotherexample, the dimensions A1 and A2 are 5 microns, resulting in an LEDlargest area of 25 square microns.

Turning to FIG. 11A, a first dielectric layer 540 is disposed on LED 500and LED substrate 510 as shown in cross section. First dielectric layer540 may be any suitable material, including but not limited to siliconoxide, aluminum oxide, titanium oxide, silicon nitride, or combinationsthereof, most preferably silicon oxide. First dielectric layer 540 issubstantially transparent to light of the wavelength emitted by activelayer 516. Substantially transparent is to mean at least 70% of thelight is transmitted through the layer. First dielectric layer 540 canbe deposited by any suitable technique, such as evaporation, sputtering,CVD, or spin-on techniques, most preferably by CVD. After deposition,first dielectric layer 540 may be planarized. Planarization is theprocess by which the top surface 542 of first dielectric layer 540 isrendered substantially parallel to surface 512 of LED substrate 510.Planarization may be accomplished by any suitable technique, includingbut not limited to chemical mechanical planarization (CMP), wet chemicaletch, or plasma etch in corrosive gas, most preferably by CMP.Subsequent steps in fabrication will be described assuming that firstdielectric layer 540 of FIG. 11A has been planarized. It is to beunderstood that the fabrication could proceed without this planarizingstep. The thickness of first dielectric layer 540 is dimension T2measured between surface 512 and surface 542. Thickness T2 can bebetween 0.05 and 100 microns, most preferably about 3 microns.

A reflector layer 550 is disposed on surface 542 of first dielectriclayer 540. Reflector layer 550 will direct more of the light emitted byLED 500 towards the viewer in the finished light emitting device. In alater step, this structure will be inverted in the final completeddevice. Reflector layer 550 may comprise any suitable material thatsubstantially reflects visible light of the wavelength emitted by activelayer 516 including but not limited to aluminum, gold, or silver, alloysof aluminum, gold, or silver, a composite material such as a polymermixed with metal oxide particles, combinations thereof, or a distributedBragg reflector (DBR), most preferably a DBR. A DBR includes one or morepairs of dielectric layers (not shown). Each dielectric layer in a pairhas a different index of refraction. The dielectric layers of the DBRmay be deposited by any suitable method, including evaporation,sputtering, CVD, or ALD, most preferably by evaporation. The thicknessof each dielectric layer in the DBR is designed to be about one quarterof the wavelength of light that is to be reflected. The wavelength oflight varies with the index of refraction of each material. For example,for an active layer of an LED that emits blue light with a wavelengthfrom 440 to 460 nm, a suitably reflective DBR would be comprised of oneto ten, most preferably five, pairs of aluminum oxide (index ofrefraction is 1.5 to 1.7) and titanium oxide (index of refraction is 2.3to 2.7) layers, where the aluminum oxide layer is 67±7 nm thick and thetitanium oxide layer is 49±5 nm thick. A reflector layer 550 that is aDBR may comprise silicon oxide, silicon nitride, aluminum oxide,tantalum oxide, or titanium oxide, or any other suitable dielectricmaterials. In other embodiments, a reflector layer is not disposed onfirst dielectric layer 540. Subsequent steps in the fabrication will bedescribed assuming the reflector layer 550 exists. While reflector layer550 is shown as a continuous layer in FIG. 11A, it is to be understoodthat the reflector layer 550 may not be continuous in all embodiments,and there may be multiple reflector layers in other embodiments.

Turning to FIG. 11B, a second dielectric layer 560 is disposed onreflector layer 550. Second dielectric layer 560 may be any suitablematerial, including but not limited to silicon oxide, aluminum oxide,titanium oxide, silicon nitride, or combinations thereof, mostpreferably silicon oxide. Second dielectric layer 560 can be depositedby any suitable means, such as evaporation, sputtering, CVD, or spin-ontechniques, most preferably by CVD. The thickness of second dielectriclayer 560 may be between 0.05 and 10 microns, most preferably about 0.2microns.

Next, an LED vertical interconnect is formed. A masking layer such asphotoresist (not shown) is applied and patterned, and portions of layers560, 550, and 540 are removed by etching in specific locations. At leasta portion of LED contact 530 is exposed after this etch is complete. Theetching may be accomplished by any suitable etchant, such as corrosivegases like CHF₃, SF₆, HBr, or wet chemical acid, such as hydrofluoricacid (HF), nitric acid (HNO₃), or sulfuric acid (H₂SO₄), most preferablyby corrosive gas. The masking layer is then removed, leaving a cavity.LED vertical interconnect 506 is then formed in the cavity. In oneembodiment, LED vertical interconnect 506 is cylinder-shaped, with thediameter of the cylinder in contact with LED contact 530, although anysuitable shape may be used. In one example, the diameter of LED verticalinterconnect 506 is 0.8 microns, although any suitable size may be used.LED vertical interconnect 506 may comprise any suitable material whichis conductive, including but not limited to ITO, AZO, FTO, or aconductive polymer such as Poly(3,4-ethylenedioxythiophene, or PEDOT),titanium, titanium nitride, tungsten, tantalum, tantalum nitride,copper, or aluminum. LED vertical interconnect 506 forms a substantiallyohmic contact to LED contact 530. LED vertical interconnect 506 may bedeposited by any suitable technique, including but not limited toevaporation, CVD, sputtering, solution deposition, or spray pyrolysis,most preferably CVD. Portions of LED vertical interconnect 506 that aredeposited on surface 562 of second dielectric layer 560 may be removedby any suitable technique, including but not limited to CMP, wetchemical etch, or plasma etch in corrosive gas, most preferably by CMP.

Turning to FIG. 11C, a third dielectric layer 570 is deposited on seconddielectric layer 560. Third dielectric layer 570 may be any suitablematerial, such as silicon oxide, aluminum oxide, titanium oxide, siliconnitride, or combinations thereof, most preferably silicon oxide. Thirddielectric layer 570 can be deposited by any suitable means, such asevaporation, sputtering, CVD, or spin-on techniques, most preferably byCVD. The thickness of third dielectric layer 570 may be between 0.05 and10 microns. Next, a masking layer such as photoresist (not shown) isapplied and patterned, and at least a portion of third dielectric layer570 is removed by etching in specific locations, leaving a cavity. Atleast a portion of LED vertical interconnect 506 is exposed after thisetch is complete. The etching may be accomplished by any suitableetchant, such as corrosive gases like CHF₃, SF₆, HBr, or wet chemicalacid, such as hydrofluoric acid (HF), nitric acid (HNO₃), or sulfuricacid (H₂SO₄), most preferably by corrosive gas. The masking layer (notshow) is then removed. Conductive material is then deposited in thecavity created in third dielectric layer 570. After deposition, theconductive material on surface 572 of fourth dielectric layer 570 may beremoved by any suitable technique, including but not limited to CMP, wetchemical etch, plasma etch in corrosive gas, most preferably by CMP,leaving a bond pad 460 in the cavity of fourth dielectric layer 570. Theconductive material for bond pad 460 may be deposited by any suitabletechnique, including but not limited to evaporation, CVD, sputtering,solution deposition, electrodeposition, or spray pyrolysis. Examples ofconductive materials for bond pad 460 include but are not limited totitanium, titanium nitride, tungsten, tantalum, tantalum nitride,copper, and aluminum. In one embodiment, bond pad 460 comprises layersof titanium, tantalum nitride, and copper. Bond pad 460 forms asubstantially ohmic contact to LED vertical interconnect 506. Fourthdielectric layer 570 and bond pad 460 are known as a bond pad layer.Bond pad layers are used throughout this application, and all follow thesame basic fabrication sequence described above. LED apparatus 580fabrication is now substantially complete.

A different embodiment of an LED apparatus is shown in FIG. 12. LEDapparatus 590 has two LED vertical interconnects 506 and 508 contactingconductive layers 518 and 514, respectively, through LED contacts 530 aand 530 b.

IB. Transistors

One part of a control apparatus, the transistors, and their fabricationmethod is now described. It is to be understood that fabrication of manymore control apparatus than is shown can be occurring simultaneously onthe transistor substrate. It is to be understood that any suitablesingle crystal transistors may be used, including but not limited tofield effect transistors or bipolar transistors. By using single crystalsemiconductor for the channel of the transistor, a higher carriermobility is obtained compared to thin film transistors. Turning to FIG.13A, transistors are fabricated in transistor substrate 100. Transistorsubstrate 100 may be any suitable single crystal semiconductor material,including but not limited to single crystal silicon, single crystalgermanium, single crystal gallium arsenide, or single crystal galliumnitride, most preferably single crystal silicon. Transistor substrate100 may comprise an etch-stop layer (not shown). The bottom surface 104of the transistor substrate 100 is referred to as the initial bottomsurface, because, in a later step, a portion of transistor substrate 100including the initial bottom surface 104 will be removed, resulting in adifferent bottom surface. The etch-stop layer (not shown) may be anysuitable material that has a substantially slower etch rate thantransistor substrate 100. In one embodiment, the etch-stop layer may besilicon oxide, as provided by silicon-on-insulator (SOI) technology. Inanother embodiment, the etch-stop layer may be boron-doped silicon. Aboron-doped silicon layer may be deposited as part of a thickerepitaxial layer deposition on a single crystal silicon wafer thatcomprises undoped silicon layers. The purpose of the etch-stop layerwill be discussed in subsection IF.

Conductive regions 120 a-e are formed in top surface 102 of transistorsubstrate 100. One method to form conductive regions 120 a-e is bydoping a portion of the transistor substrate 100 to be either p-type orn-type. It may be doped by any suitable technique, for example, byapplying a masking layer (not shown), patterning, and then implantingions. The masking layer is then removed. An anneal may activate theimplanted ions. Conductive regions 120 a-e are more conductive than thesurrounding silicon substrate 100.

The conductive regions 120 may further comprise a silicide layer. Thesilicide layer may be formed on conductive regions 120 a-e to furtherdecrease the resistance, form ohmic contacts, and/or form an etch-stoplayer for subsequent steps. A silicide layer is formed by deposition ofa metal, including but not limited to titanium, cobalt, nickel, ortungsten, and then annealing at elevated temperature (above 400° C.) toreact the metal with silicon to form a silicide film, for example,titanium silicide, cobalt silicide, nickel silicide, or tungstensilicide. An example of a silicide layer is shown as 122 a. In otherembodiments, a silicide layer is not a part of the conductive regions.

Conductive regions 120 a-e may be isolated from one another electricallyby dielectric regions 130 formed in top surface 102 of transistorsubstrate 100, in some embodiments. Dielectric regions 130 may be formedby shallow trench isolation (STI), field oxidation (FOX), or any othersuitable dielectric region formation technique.

First transistor 200 comprises conductive region 120 b, which may be asource or drain, conductive region 120 c, which may be a source or adrain, a dielectric gate layer 210 a, a conductive gate layer 220 a, anda portion of transistor substrate 100 between conductive regions 120 band 120 c which is the channel. The dimensions SD1 and SD2 of conductiveregions 120 b and 120 c, respectively, may be from about 0.05 to 20microns, for example about 0.5 microns. The dimension G1, which may bereferred to as the gate length, may be from about 0.05 to 5 microns, forexample about 1.0 micron. In one example, if dimensions SD1 and SD2 are0.5 microns and dimension G1 is 1.0 microns, transistor 200 will have atotal length of about 2.0 microns. Dielectric gate layer 210 a maycomprise silicon oxide, silicon nitride, aluminum oxide, hafnium siliconoxide nitride, hafnium silicon oxide, combinations therein, or any othersuitable material. The thickness of dielectric gate layer 210 a may bebetween 0.001 and 0.5 microns thick, for example about 0.02 microns.Conductive gate layer 220 a may comprise any suitable material,including but not limited to conductive silicon, titanium nitride,tantalum, or tantalum nitride. Sidewall spacers 230 may exist on thesidewalls of conductive gate layers 220, one example of which isidentified in FIG. 13A. Second transistor 300 comprises similar elementsas first transistor 200, although the materials and dimensions of secondtransistor 300 may be the same as or different than those of firsttransistor 200. In one embodiment, transistor 300 also has a totallength of about 2 microns. Including some of the length of the adjacentdielectric regions 130, the total length 2TL of transistors 200 and 300may be about 5 microns in this example. Other elements of single crystaltransistors, such as lightly doped drains (LDD), are not described orshown herein but are well known to those skilled in the art and may beincorporated in other embodiments.

Turning to FIG. 13B, after transistor fabrication, fifth dielectriclayer 310 is disposed on transistors 200 and 300, conductive regions 120a-e, dielectric layers 130, and transistor substrate 100. Fifthdielectric layer 310 may be any suitable material, including but notlimited to silicon oxide, silicon nitride, or aluminum oxide, mostpreferably silicon oxide. Fifth dielectric layer 310 is deposited by anysuitable technique, including evaporation, sputtering, spin on, or CVD,most preferably CVD. Fifth dielectric layer may be any suitablethickness, for example between 0.1 and 2 microns. In one embodiment thethickness is 0.2 microns. Top surface 312 of fifth dielectric layer 310can be rendered substantially parallel to top surface 102 of transistorsubstrate 100. Subsequent steps in fabrication will be describedassuming that surface 312 of fifth dielectric layer 310 shown in FIG.13B has been planarized. It is to be understood that the fabricationcould proceed without this planarizing step.

Transistor vertical interconnects are fabricated next. Transistorvertical interconnects form ohmic contacts to some or all of conductiveregions 120 and conductive gate layers 220. Transistor verticalinterconnects 240 a, 240 b, 242 a, 242 b, and 244 may be fabricated byany suitable technique. One example of transistor vertical interconnectfabrication is to deposit a masking layer (not shown), pattern themasking layer, and etch portions of fifth dielectric layer 310, exposingat least a portion of conductive regions 120 a, 120 c, and 120 d andconductive gate layers 220 a and 220 b. The masking layer is thenremoved. Any suitable transistor vertical interconnect material,including but not limited to aluminum or tungsten, or a stack oftitanium, titanium nitride, and aluminum, or a stack of titanium,titanium nitride, and tungsten, is deposited into the cavities whereportions of fifth dielectric layer 310 were removed. The portions oftransistor vertical interconnect material on surface 312 are removed byany suitable technique such as etchback or CMP, leaving transistorvertical interconnect material in the cavities of fifth dielectric layer310. A via etch-stop layer 320 is then deposited on surface 312 of fifthdielectric layer 310. Via etch-stop layer 320 may be any suitablematerial, for example silicon nitride. Via etch-stop layer 320 may bedeposited by any suitable technique, including evaporation, sputtering,spin on, or CVD, most preferably CVD, and may have any suitablethickness, for example 50 nm.

IC. Stack Capacitor

The stack capacitor (as shown in FIG. 5) and fabrication will now bedescribed. In this application, a stack capacitor is above one of thetransistors and has a longest dimension substantially orthogonal to thetop surface of the transistor substrate. Turning to FIG. 13C, a sixthdielectric layer 330 is deposited on via etch-stop layer 320. Sixthdielectric layer 330 may be any suitable material, for example siliconoxide. Sixth dielectric layer 330 may be deposited by any suitabletechnique, including evaporation, sputtering, spin on, or CVD, mostpreferably CVD, and may be any suitable thickness, for example 2microns. A masking layer (not shown) is then deposited and patterned,and portions of sixth dielectric layer 330 and via etch-stop layer 320are removed by etching, leaving a cavity in sixth dielectric layer 330and via etch-stop layer 320, and exposing at least a portion oftransistor vertical interconnect 242 b. The masking layer is thenremoved. A lower stack capacitor electrode layer 350 is then depositedin the cavities of sixth dielectric layer 330 and etch-stop layer 320.Lower stack capacitor electrode layer 350 and transistor verticalinterconnect 242 b are connected electrically. Any suitable material maybe used for lower stack capacitor electrode layer 350, including but notlimited to doped polysilicon, titanium nitride, platinum, tantalum,molybdenum, or cobalt, or combinations therein. Lower stack capacitorelectrode layer 350 may be deposited by any suitable technique,including but not limited to evaporation, sputtering, or CVD, and mayhave any suitable thickness from about 5 nm to 500 nm, for example about20 nm. A masking layer (not shown) is then deposited and patterned, andthe portions of lower capacitor electrode layer 350 on surface 332 areetched, leaving the structure as shown in FIG. 13C. The masking layer isremoved.

Turning to FIG. 13D, sixth dielectric layer 330 and via etch-stop layer320 are removed by selective etching. In one embodiment (referring toboth FIGS. 13C and 13D), sixth dielectric layer 330 may comprise siliconoxide and via etch-stop layer 320 may comprise silicon nitride, andlower stack capacitor electrode layer 350 may comprise dopedpolysilicon. Dilute hydrofluoric acid will etch silicon oxide rapidlywhile etching silicon nitride and doped polysilicon slowly. After sixthdielectric layer 330 is removed by dilute hydrofluoric acid etch, viaetch-stop layer 320 can then be removed selectively by etching in hotphosphoric acid. Hot phosphoric acid will etch silicon nitride rapidlywhile etching silicon oxide and doped polysilicon slowly.

Turning to FIG. 13E, a capacitor dielectric layer 360 is then depositedon lower stack capacitor electrode layer 350. Capacitor dielectric layer360 may be deposited by any suitable technique, including evaporation,sputtering, and CVD, and may have any suitable thickness from about 5 nmto 100 nm, for example about 10 nm. Capacitor dielectric layer 360 maycomprise any suitable material or combination of materials, includingbut not limited to silicon oxide, silicon nitride, hafnium oxide,zirconium oxide, or aluminum oxide. A masking layer (not shown) is thendeposited and patterned, and portions of capacitor dielectric layer 360are removed by etching. An upper stack capacitor electrode layer 370(patterned in a later step into sections 370 a and 370 b, as shown) isthen deposited on capacitor dielectric layer 360. Upper stack capacitorelectrode layer 370 may be deposited by similar techniques, have similarthickness, and comprise similar or different materials as lower stackcapacitor electrode layer 350. A masking layer (not shown), is thendeposited and patterned, and portions of upper stack capacitor electrodelayer 370 are removed by etching, creating portions 370 a and 370 b. Themasking layer is then removed. Capacitor 400S fabrication is nowsubstantially complete. A seventh dielectric layer 380 is deposited overcapacitor 400S and planarized. The vertical orientation of stackcapacitor 400S has a small footprint. Upper stack capacitor electrodelayer portion 370 a is electrically connected to transistor verticalinterconnects 242 a and 240 b as well as capacitor dielectric layer 360,as shown in FIG. 13D. Transistor vertical interconnect 242 a iselectrically connected to conductive region 120 c, which is the sourceor drain of transistor 200. Lower stack capacitor electrode layer 350 iselectrically connected to transistor vertical interconnect 242 b.Transistor vertical interconnect 242 b is electrically connected toconductive region 120 d, which is the source or drain of transistor 300.Through the connections described above, capacitor 400S is in operativecommunication with first transistor 200 and second transistor 300. Upperstack capacitor electrode layer portion 370 b electrically connectstransistor vertical interconnects 244 and 240 a. Upper stack capacitorelectrode layer portion 370 b may also be referred to as a horizontalinterconnect.

Transistor vertical interconnect 410 is formed in seventh dielectriclayer 380 and sixth dielectric layer 310 by techniques similar to thosedescribed earlier for transistor vertical interconnects 244 and 242 aand 242 b. A bond pad layer comprising eighth dielectric layer 420 and abond pad 430 is then formed on seventh dielectric layer 380. Controlapparatus 480 fabrication is now substantially complete.

ID. Trench Capacitor

A different embodiment of the fabrication of the control apparatusemploying a trench capacitor is now described. In this application atrench capacitor is at least partially formed in the transistorsubstrate and has a longest dimension orthogonal to the top surface ofthe transistor substrate. The description of transistor fabrication iscondensed, as much of the previous more detailed description oftransistor fabrication is applicable to this embodiment. Turning to FIG.14A, a pad oxide layer 110 is first deposited or grown on transistorsubstrate 100. Pad oxide layer 110 may be any suitable thickness, forexample about 10 nm, and may comprise silicon oxide. A masking layer(not shown), is applied and patterned, and a cavity 114 is etched in padoxide layer 110 and a portion of transistor substrate 100. The maskinglayer is then removed. A conductive region is then formed in transistorsubstrate 100 where the etch has exposed transistor substrate 100. Thisconductive region is lower trench capacitor electrode 116. Lower trenchcapacitor electrode 116 is formed by doping the exposed portion oftransistor substrate 100. The doping may be n-type or p-type and may beaccomplished by any suitable method. One method is by exposingtransistor substrate 100 to a dopant containing gas such as phosphine orboron trichloride at an elevated temperature, for example greater than700° C. Phosphorus or boron atoms will diffuse into transistor substrate100. Another method is to deposit a dopant-containing material, such asphosphorous silicate glass (PSG), into cavity 114 in transistorsubstrate 100 and anneal at an elevated temperature, for example greaterthan 700° C., and then remove the PSG material by selective etching.This will cause phosphorus atoms to diffuse from the PSG material intotransistor substrate 100. With either doping method, pad oxide layer 110prevents the non-exposed portions of transistor substrate 100 from beingdoped. Referring to both FIGS. 14A and 14B, after lower trench capacitorelectrode 116 is formed. Pad oxide layer 110 is then removed byselective etching, by, for example dilute hydrofluoric acid. A moldnitride layer 117 is then deposited in the remainder of cavity 114. Moldnitride layer 117 may comprise silicon nitride deposited by CVD. Theportions of mold nitride layer 117 on surface 102 may be removed by anetch, which does not remove the portion of mold nitride layer 117 in thecavity.

Turning to FIG. 14C, transistors 200 and 300 are formed in top surface102 of transistor substrate 100 using the fabrication techniquesdescribed earlier. Conductive region 120 d of transistor 300 and lowertrench capacitor electrode 116 are electrically connected aftertransistor fabrication. Referring to FIGS. 14C and 14D, fifth dielectriclayer 310 is deposited and planarized. A masking layer (not shown) isdeposited and patterned on fifth dielectric layer 310, and a cavity isetched in fifth dielectric layer 310. The masking layer is removed. Moldnitride layer 117 is removed by selective etching. A trench capacitordielectric layer 118 and upper trench capacitor electrode layer 119 aredeposited sequentially into the cavity onto exposed lower trenchcapacitor electrode layer 116. Portions of trench capacitor dielectriclayer 118 and upper trench capacitor electrode layer 119 can be removedfrom surface 312 of fifth dielectric layer 310 by CMP or etching,leaving the structure shown in FIG. 14D.

Turning to FIG. 14E, transistor vertical interconnects 244, 240 a, 242a, 240 b, and 410, seventh dielectric layer 380, bond pad 430 and eighthdielectric layer 420 are formed by similar techniques as describedearlier. In addition, horizontal interconnects 374 a and 374 b areformed in seventh dielectric layer 380. Horizontal interconnect 374 aconnects transistor vertical interconnect 244 to transistor verticalinterconnect 240 a. Horizontal interconnect 374 b connects transistorvertical interconnects 242 a and 240 b, and upper trench capacitorelectrode 119. Control apparatus 490 fabrication with trench capacitor400T is now substantially complete. The vertical orientation of trenchcapacitor 400T gives it a small footprint.

IE. Bonding the Control Apparatus to the LED Apparatus

Turning to FIG. 15A, in one embodiment LED apparatus 580 (with a singleLED vertical interconnect, shown in FIG. 11C) is flipped over and bondedto control apparatus 480 (with a stack capacitor, shown in FIG. 13E),with the two bonded apparatus shown in FIG. 15B. In other embodimentsLED apparatus 590 (with two LED vertical interconnects, shown in FIG.12) and/or control apparatus 490 (with a trench capacitor, shown in FIG.14E) may be used in the bonding. The technique is sometimes referred toas flip-chip bonding as the devices on each respective substrate faceone another, and transistor substrate 100 and LED substrate 510 are theoutermost surfaces of the bonded pair. Any suitable bonding techniquemay be used, including but not limited to hybrid bonding,thermocompression bonding, anodic bonding, plasma activated bonding,eutectic bonding, or surface activated bonding, most preferably hybridbonding. The bond formed between two structures may be: wafer-to-wafer,in which two wafers each with multiple die are bonded to one another;die-to-wafer, in which a die or dies are bonded to a wafer; ordie-to-die, in which a die is bonded to another die. A wafer usuallycomprises multiple die. Hybrid wafer bonding or hybrid die bondingdescribes the joining of two surfaces, wherein at least one of the twosurfaces comprises at least two different materials. In one example ofhybrid bonding, the two surfaces are brought into contact under pressureand heated to achieve a bond of the two surfaces.

As shown in FIG. 15B, surface 572 of LED apparatus 580 is in contactwith surface 422 of control apparatus 480 after bonding. The largestarea of LED 500 now overlies first transistor 200, second transistor300, and capacitor 400S. LED 500 is in operative communication withtransistor 300 through the connections of transistor verticalinterconnect 410, bond pads 430 and 460, and LED vertical interconnect506, and LED contact 530. Reflector layer 550 is disposed between LED500 and transistor substrate 100. It is important to note that LEDapparatus 580 is not connected to control apparatus 480 through wirebonds, which are common in the prior art. Wire bonds are interconnectsthat join two devices by a wire that was mechanically placed and bondedto the two devices using downward pressure and ultrasonic energy and/orheat. The wires in wire bonds are typically 15 microns in diameter orlarger and have metal balls at either end that are larger than 15microns in diameter.

IF. Through Substrate Interconnects

Until this point in the fabrication sequence of this embodiment, bothLED substrate 510 and transistor substrate 100 have remained fullyintact, as shown in FIG. 15B. Both LED substrate 510 and transistorsubstrate 100 may be about 500 microns thick, although they may be anysuitable thickness that allows for mechanical handling duringfabrication. This thickness imparts mechanical stability to therespective substrates and allows the plurality of devices to be handledduring fabrication. With two thick substrates bonded together, one ofthe two substrates can now be removed in whole or in part, and thestructure will retain mechanical stability for handling with onesubstrate intact.

Turning to FIGS. 16A and 16B, a portion of transistor substrate 100 isnow removed. Transistor substrate 100 in FIG. 16A has an originalthickness TS1. A portion of transistor substrate 100 can be removed byany suitable wafer thinning technique, including but not limited tolaser lift off, mechanical polishing, or chemical etch. In oneembodiment, mechanical polishing may be combined with chemical etch toremove a thickness of the transistor substrate 100, with resultanttransistor substrate thickness TS2 shown in FIG. 16B. Thickness TS2 issubstantially less than thickness TS1. Due to the scale of FIGS. 16A andB, the thickness of transistor substrate 100 removed is not accuratelyshown. By combining mechanical polishing with chemical etching, a moreprecise thickness of transistor substrate 100 may be removed at lowercost and with greater precision in the remaining substrate thicknessthan if either technique was used alone. For example, mechanicalpolishing may first remove about 400 microns of an initial 500micron-thick dimension TS1 of transistor substrate 100, resulting in apost-polish transistor substrate thickness of about 100 microns. Forwafer thinning by polishing, the wafer is rotated about its center on asurface with abrasive media. Wafer thinning by mechanical force issometimes referred to as grinding when the remaining substrate surfaceis rough, and polishing when the remaining substrate surface is smooth.Either grinding or polishing, or a combination, may be used. Aftergrinding and/or polishing, a chemical etch may then remove about 95microns of the remaining 100 microns, leaving 5 microns (dimension TS2)of transistor substrate 100. Chemical etch of transistor substrate 100may be accomplished by any suitable chemistry. For example, KOH, TMAH,HF+HNO₃, or HF+NH₄F chemistries may be used to etch silicon substrates.An etch-stop layer in transistor substrate 100 (not shown) may act toslow or stop the rate of substrate grinding, polishing, or etching sothat the remaining thickness TS2 of transistor substrate 100 may bereliably determined. For example, if KOH is used to etch silicon, KOHwill etch undoped silicon about 20× faster than a heavily boron-dopedsilicon etch-stop layer. The boron-doped layer of silicon acts as anefficient etch-stop for silicon etching. If silicon oxide is used as theetch-stop layer, KOH will etch silicon about 500× faster than it willetch silicon oxide. The silicon oxide layer acts as an efficientetch-stop for silicon etching. Initial bottom surface 104 of transistorsubstrate 100 is removed. Referring to FIG. 16B, after removal of aportion of transistor substrate 100, the remaining portion of transistorsubstrate 100 designated by dimension TS2 remains and has a bottomsurface 106. The final thickness TS2 of transistor substrate 100 may beany suitable dimension from 0.1 to 100 microns, most preferably lessthan 20 microns. Reducing the value of TS2 to less than 20 micronsfacilitates formation of through substrate interconnects with smallsize.

By removing most of the original transistor substrate 100, throughsubstrate interconnects with small features can now be fabricated in theremaining transistor substrate 100. Turning to FIG. 16C, throughsubstrate interconnects are fabricated by first masking and etchingcavities in transistor substrate 100. The cavities in substrate 100expose a portion of conductive regions 120 a, 120 b, and 120 d. Portionsof transistor substrate 100 may be etched by any suitable etchant,including corrosive gases or chemical acids, most preferably bycorrosive gases. The masking layer (not shown) is then removed. In oneembodiment, after etching, a sidewall dielectric layer 142 may be formedon the sidewalls of the cavities in transistor substrate 100. Sidewalldielectric layer 142 will insulate the sidewalls of the transistorsubstrate 100 from the subsequently formed through substrateinterconnects. Sidewall dielectric layer 142 may comprise any suitablematerial, including but not limited to silicon oxide or silicon nitride,most preferably silicon oxide. Sidewall dielectric layer 142 may bedeposited by any technique with good step coverage, most preferably byCVD. Portions of sidewall dielectric layer 142 that is deposited onconductive regions 120 can be removed by an anisotropic etch. Thisanisotropic etch will remove dielectric layer 142 from the surface ofconductive region 120 while leaving it on the sidewalls of transistorsubstrate 100. This process allows the through substrate interconnectthat follows to make electrical contact to the conductive regions 120while being insulated from transistor substrate 100. The remainingportions of sidewall dielectric layer 142 are shown in FIG. 16C. Inother embodiments, a sidewall dielectric layer is not needed on thesidewalls of the cavities in transistor substrate 100, for example whentransistor substrate 100 is not substantially conductive.

Turning to FIG. 16D, through substrate interconnect material isdeposited in the cavities of transistor substrate 100. The throughsubstrate interconnect material may comprise any suitable material,including but not limited to aluminum, copper, or tungsten, or a stackof titanium, titanium nitride, and aluminum layers, or a stack oftitanium, titanium nitride, and tungsten layers, or a stack of titanium,tantalum nitride, and copper layers. Any suitable method for throughsubstrate interconnect deposition may be used, such as evaporation,sputtering, electrodeposition, or CVD. Through substrate interconnectmaterial on surface 106 can be removed by etching or CMP, mostpreferably by CMP, leaving through substrate interconnects 140 as shownin FIG. 16D.

A bond pad layer is formed on surface 106, resulting in bond pads 160 inninth dielectric layer 150. Bond pads 160 are connected to throughsubstrate interconnects 140. LED substrate 510 remains on the apparatusat this point in fabrication to allow for mechanical handling of thebonded apparatus.

IG. Bonding the Paired LED+Control Apparatus to a Backboard

Turning to FIG. 17, the LED+control apparatus pair is bonded to thebackboard 600. Backboard 600 comprises a backboard substrate 610 with aplurality of bond pads 620 and a plurality of backboard interconnects630. Backboard 600 may comprise a printed circuit board (PCB) or aninterposer. An interposer may comprise a silicon oxide or siliconsubstrate, and will have a smooth surface 602 compared to a PCB. Thesurface roughness of surface 602 will be less than 0.2 microns root meansquare for an interposer. The surface roughness of a PCB made of FR-4may exceed 5 microns root mean square. The small surface roughness of aninterposer allows the patterning by lithography of fine features lessthan 0.5 micron in size, such as the plurality of backboardinterconnects 630. In one embodiment, backboard 600 may comprise aninterposer, and backboard interconnects 630 may be fabricated by adamascene process in silicon oxide. Backboard interconnects 630 maycomprise copper or any suitable conductive material. Backboardinterconnects 630 are shown as a single layer in FIG. 17. In otherembodiments, backboard interconnects 630 may be fabricated as multiplelayers. In a different embodiment, backboard 600 may comprise a printedcircuit board (PCB) with the backboard substrate 610 comprising FR-4material and backboard interconnects 630 comprising copper. Aninterposer can generally provide smaller feature sizes and pitches ofbackboard interconnects compared with a PCB, and an interposer ispreferred for this reason. The interposer may comprise additionalaspects (not shown), such as adhesive metal layers, micro bumpconnections, ball or stud bumps, or copper paste, or any suitablefeature.

After bonding, backboard interconnects 630 are connected electrically tocontrol apparatus 480. Any suitable bonding technique may be used tojoin the backboard 600 to the control apparatus 480, including but notlimited to thermocompression bonding, adhesive bonding, anodic bonding,plasma activated bonding, eutectic bonding, or surface activatedbonding, most preferably thermocompression bonding. Other techniques maybe used to physically and connect backboard 600 to control apparatus480, including but not limited to ball or stud bumping and copperpasting. The principles and mechanisms of bonding are well known tothose skilled in the art.

IH. Formation of Wavelength-Converting Layer

Turning to FIG. 18A, backboard 600 now provides mechanical stability tothe structure comprising backboard 600, control apparatus 480, and LEDapparatus 580. The LED substrate can now be removed from this structure.LED substrate 510, shown in FIG. 17 is removed, as shown in FIG. 18A.LED substrate 510 may be removed by a laser process. If LED substrate510 is sapphire, a KrF Excimer laser with an energy density of 400mJ/cm², a wavelength of 248 nm, and a pulse width of 38 ns can irradiatethe sapphire surface at an elevated temperature of 60° C. and remove thesapphire substrate from first conductive layer 514 shown in FIG. 18A.LED substrate 510 may be removed by chemical etching. If LED substrate510 is GaAs, a solution of NH₄OH:35H₂O or a solution of5H₃PO₄:3H₂O₂:3H₂O can be applied to remove the GaAs substrate from firstconductive layer 514. If LED substrate 510 is silicon, a solution ofKOH, TMAH, HF+HNO₃, or HF+NH₄F can be applied to remove LED substrate510 from first conductive layer 514.

After the LED substrate is removed, surface 515 of first conductivelayer 514 may be roughened to enhance light extraction from LED 500. Forexample, if first conductive layer 514 is GaN or AlGaInN, surface 515can be roughened by etching in a solution of KOH. If first conductivelayer 514 is GaP, AlGaP, or AlGaNInP, a solution of HCl and H₃PO₄ canroughen surface 515. If first conductive layer 514 is GaP, a corrosivegas mixture of BCl₃, Cl₂, and Ar can roughen surface 515. The roughnessof surface 515 is exaggerated for clarity. For example, surface 515 mayhave a root mean square roughness of about 0.2 microns. In otherembodiments, first conductive layer 514 is not roughened.

Turning to FIG. 18B, a transparent conductive layer 576 is deposited onfirst conductive layer 514 of LED 500. Transparent conductive layer 576may be any suitable material that is substantially transparent tovisible light and is relatively conductive to electricity, including butnot limited to indium tin oxide (ITO), aluminum zinc oxide (AZO),fluorine-doped tin oxide (FTO), or a stack of a thin nickel layerfollowed by a thin gold layer. Transparent conductive layer 576 may bedeposited by any suitable technique, such as evaporation, CVD, orsputtering, most preferably evaporation. An interconnect (not shown),may connect transparent conductive layer 576 to a backboard interconnecton backboard 600. Transparent conductive layer 576 may be patterned andetched (not shown).

Wavelength-converting layer 578 is next deposited on transparentconductive layer 576. Wavelength-converting layer 578 overlies LED 500.Wavelength-converting layer 578 is excited by the light emitted by theactive layer 516 and emits light of a different wavelength than isemitted by active layer 516. In a specific embodiment,wavelength-converting layer 578 may comprise an organic material, forexample silicone, epoxy, or polycarbonate, combined with inorganicphosphor particles such as GaAlN, with the GaAlN phosphor particlesexcited by light with a dominant wavelength of between 420 and 470 nm(blue) and emitting light with a dominant wavelength of between 500 and550 nm (red). In different embodiment, the phosphor particles may beCaAlSiN:Eu, with CaAlSiN:Eu phosphor particles excited by light with adominant wavelength of between 420 and 470 nm (blue), and emitting lightwith a dominant wavelength of between 610 and 730 nm (green). Anysuitable phosphor particle may be used. In a different embodiment,silicone, epoxy, or polycarbonate may be combined with quantum dots, thequantum dots being nano-scale semiconductor material, for example groupII-VI material having a composition ZnCdMgSe, CdSe, InP, or ZnS. In oneembodiment, the composition of the quantum dots can be optimized to emitred (500 to 550 nm) or green (610 to 730 nm) light when excited by bluelight (420 to 470 nm). Any suitable quantum dot composition may be used.In one embodiment, wavelength-converting layer 578 may be screen printedinto any suitable pattern on the wafer.

In a different embodiment, wavelength-converting layer 578 may bephosphor particles or quantum dots embedded in glass, a technique knownas phosphor-in-glass (PiG) or quantum dot-in-glass (QDiG). For example,glass paste combining SiO₂, B₂O₃, phosphor particles or quantum dots,adhesive, and organic solvent may be screen printed onto transparentconductive layer 576. The screen printing may be done with a stencilpattern or without patterning. Volatile organic components of the glasspaste may be removed by drying at 150° C. and sintering at 600° C. In adifferent embodiment, the PiG or QDiG layer may be deposited by aspin-on technique, in which chemicals and phosphor particles or quantumdots are suspended in organic solvents. The solution is spun ontotransparent conductive layer 576 as a film. The film is dried andannealed, which substantially removes the organic materials, leaving aglass film with phosphor particles or quantum dots. The glass film withphosphor particles or quantum dots is wavelength-converting layer 578.If the wavelength-converting layer 578 was not initially patternedduring deposition, a masking layer (not shown) can be applied,patterned, and wavelength-converting layer 578 etched to form a pattern.Wavelength-converting layer 578 may be etched by any suitable etchant,including but not limited to acids or corrosive gases. The masking layeris removed.

Turning to FIG. 19A, in yet another embodiment, wavelength-convertinglayer 578 may comprise multiple quantum wells (MQWs). Quantum wells aretwo dimensional films of inorganic semiconductors, and comprise pairs ofalternating films of different materials, for example, ZnCdSe/ZnSe,ZnCdSe/ZnCdMgSe, InGaN/GaN, AlGaNInP/GaNInP, or any suitable pairing.Wavelength-converting layer 578 comprising MQWs of GaInN/GaN are grownon a thick n-type GaN layer 810 on a sapphire substrate 800.Wavelength-converting layer 578, GaN layer 810, and sapphire substrate800 are flipped over and wavelength-converting layer 578 is bonded totransparent conductive layer 576, as shown in FIG. 19B. GaN layer 810and sapphire substrate 800 are then removed by similar substrate removaltechniques as described earlier. Wavelength-converting layer 578 can bepatterned (not shown) and etched, either before or after bonding to thestructure comprising the LED. In one example, GaInN/GaN MQW films inwavelength-converting layer 578 absorb blue light from active layer 516and emit green light. In another example, AlGaNInP/GaNInP MQW films inwavelength-converting layer 578 absorb blue light from active layer 516and emit red light.

In another embodiment shown in FIG. 19C, a tenth dielectric layer 794can be disposed between transparent conductive layer 576 andwavelength-converting layer 578. Tenth dielectric layer 794 may havebetter adhesion to subsequently bonded wavelength-converting layer 578compared with transparent conductive layer 576. Tenth dielectric layer794 may any suitable material, including but not limited to siliconoxide, silicon nitride, aluminum oxide, or titanium oxide. A passivatinglayer 796 is deposited on wavelength-converting layer 578. Passivatinglayer 796 protects the light emitting device from moisture intrusionand/or mobile ions which might degrade it. Passivating layer 796 can beany suitable material which is substantially transparent to light of thewavelength emitted by the active layer of the LED and/or the wavelengthemitted by the wavelength-converting layer 578. If wavelength-convertinglayer 578 contains organic materials, which are sensitive to elevatedtemperature, passivating layer 796 can be an organic material, includingbut not limited to silicone, epoxy, or polycarbonate. Use of an organicmaterial for passivating layer 796 can avoid high temperature processingthat could compromise wavelength-converting layer 578 ifwavelength-converting layer 578 was organic. If wavelength-convertinglayer 578 is PiG or QDiG, both of which are less sensitive to elevatedtemperature than an organic material such as silicone, epoxy, orpolycarbonate, then passivating layer 796 may comprise either an organiclayer such as silicone, epoxy, or polycarbonate or an inorganicdielectric material such silicon oxide, silicon nitride, aluminum oxide,or titanium oxide. The inorganic dielectric material for passivatinglayer 796 can be deposited by any suitable method, includingevaporation, sputtering, or CVD, most preferably CVD. If passivatinglayer 796 is silicon oxide, it may have a thickness between 0.02 and 10microns thick, for example about 0.5 microns. A passivating layer mayalso be deposited on wavelength-converting layer 576 in FIG. 19B,although it is not shown.

Summarizing, a method for forming a light emitting device comprises thefollowing steps: providing a transistor substrate having a top surfaceand bottom surface and the top surface comprising a plurality ofconductive regions; forming two transistors in the top surface of thetransistor substrate and a capacitor; providing an LED substrate, andforming an LED on the LED substrate wherein the LED comprises galliumnitride, indium gallium nitride, indium arsenide, aluminum galliumarsenide, gallium arsenide, gallium phosphide, gallium arsenidephosphide, aluminum indium gallium phosphide, gallium arsenide nitride,aluminum indium arsenide, aluminum antimonide, indium phosphide, indiumantimonide, or indium gallium arsenide phosphide, and combinationsthereof; forming a reflector layer; bonding the two transistors andcapacitor to the LED, wherein after bonding the reflector layer isdisposed between the LED and the two transistors and capacitor, the LEDis in operative communication with one of the two transistors, and theLED overlies the two transistors and capacitor; removing a portion ofthe transistor substrate; and forming a plurality of through substrateinterconnects, wherein each through substrate interconnect extendsthrough the transistor substrate from a conductive region of theplurality of conductive regions to the bottom surface of the transistorsubstrate.

II. Light Emitting Assembly

Some embodiments of light emitting assemblies comprising a plurality oflight emitting devices will now be described. The finished assembly maybe diced from an even larger plurality of light emitting devices. Thelight emitting assembly will be fabricated using one LED substrate andone transistor substrate with a plurality of LED apparatus and aplurality of control apparatus on each, respectively. There are manypossible shapes and configurations, and only two examples are shown,without limitation of the present invention. Fabrication of the assemblyof light emitting devices occurs similar to the description in theprevious section for a single light emitting device, with somedifference in the wavelength-converting layers.

One embodiment of a light emitting assembly is shown in cross-sectionalschematic in FIG. 20A. Assembly 900 has three light emitting devices910, 920, and 930. It is to be understood there may be many more lightemitting devices in the assembly than shown in the FIG. 20A. Althoughthe light emitting devices 910, 920, and 930 are shown with the samesize, they may each have a different size in other assembly embodiments.For example, the LEDs may of different sizes to allow for more efficientproduction of combined light output of the assembly. Assembly 900 has atransistor substrate 100 having a top surface 102 and a bottom surface106, and a plurality of conductive regions 120. Light emitting device910 is now described in more detail, although it is to be understoodthat this description can generally apply to any of the light emittingdevices. Light emitting device 910 has a plurality of through substrateinterconnects 140 which extend through transistor substrate 100 fromconductive regions 120 to the bottom surface 106 of transistor substrate100. Light emitting device 910 has a first transistor 200 and a secondtransistor 300 formed in the top surface 102 of transistor substrate100. Light emitting device 910 has a capacitor 400S, with a longestdimension C1 that is substantially orthogonal to top surface 102 oftransistor substrate 100. Capacitor 400S is in operative communicationwith first transistor 200 and second transistor 300. Light emittingdevice 910 has an LED 500, with a largest area which overliestransistors 200 and 300 and capacitor 400S. Light-emitting devices 920and 930, each have wavelength-converting layers 578 a and 578 b,respectively. In one example, first wavelength converting layer 578 aemits light with a dominant wavelength between 500 and 580 nm, andsecond wavelength converting layer 578 b emits light with a dominantwavelength between 610 and 730 nm. Assembly 900 further comprises abackboard 600. Backboard 600 comprises backboard interconnects 630.Backboard 600 provides mechanical stability and electrical connectionsto other devices. Backboard 600 may comprise a PCB or interposer. Aspreviously discussed, the smoother surface of an interposer compared toa PCB allows for the patterning by lithography of finer features, and aninterposer is preferred for this reason.

The active layer of each LED in this example may emit light ofsubstantially the same dominant wavelength, for example, light withdominant wavelength 420 to 470 nm (blue). In the embodiment shown inFIG. 20A, LED 500 of light emitting device 910 does not have awavelength-converting layer overlying the LED, and light emitting device910 will emit light of the same dominant wavelength as the active layerof LED 500. Light emitting device 920 has wavelength-converting layer578 a overlying it. First wavelength-converting layer 578 a of lightemitting device 910 may absorb light with dominant wavelength of between420 and 470 nm (blue) and emit light with a dominant wavelength ofbetween 500 and 550 nm (red). Light emitting device 930 has a secondwavelength-converting layer 578 b overlying the LED. Secondwavelength-converting layer 578 b of light emitting device 930 mayabsorb light with dominant wavelength of between 420 and 470 nm (blue)and emit light with a dominant wavelength of between 610 to 730 nm(green). In this embodiment, assembly 900 of light emitting devices mayemit red, green, or blue light, or combinations of these light colors.Assembly 900 may comprise a pixel in a color display with light emittingdevices 910, 920, and 930 as subpixels. In other embodiments, anassembly of three light emitting devices may emit cyan, magenta, oryellow, respectively, to form a pixel in a different color display. In adifferent embodiment (not shown), an assembly of light emitting deviceswould not have any wavelength-converting layers overlying them, and eachlight emitting device would emit light of the same dominant wavelength,suitable for use in a monochromatic display. The arrangement of lightemitting devices and wavelength-converting layers in an assembly may beaccomplished in any suitable manner. There may be one, two, three ormore different kinds of wavelength-converting layers in an assembly thatemit one, two, three, or more different wavelengths of light.

Summarizing, a light emitting assembly 900 has transistor substrate 100having a top surface 102 and a bottom surface 106. There is a pluralityof conductive regions 120 in top surface 102 of transistor substrate100. Light emitting assembly 900 has a plurality of light emittingdevices 910, 920, and 930. By example, light emitting device 910comprises a plurality of through substrate interconnects 140, whereineach through substrate interconnect extends through transistor substrate100 from one of the conductive regions 120 to bottom surface 106 of thetransistor substrate 100. Light emitting device 910 also comprises afirst transistor 200 and a second transistor 300 formed in top surface102 of transistor substrate 100. Light emitting device 910 alsocomprises capacitor 400S with longest dimension C1 substantiallyorthogonal to top surface 102 of transistor substrate 100. Capacitor400S is in operative communication with first transistor 200 and secondtransistor 300. Light emitting device 910 also comprises LED 500, whichhas a largest area overlying first transistor 200, second transistor300, and capacitor 400S. LED 500 is in operative communication witheither first transistor 200 or second transistor 300. Light emittingassembly 900 also comprises a plurality of wavelength-converting layers.There is at least a first wavelength-converting layer 578 a that emitslight with a dominant wavelength of between 500 and 550 nm and a secondwavelength-converting layer 578 b that emits light with a dominantwavelength of between 610 and 730 nm. Light emitting assembly 900 alsocomprises backboard 600 wherein the backboard may comprise aninterposer.

Referring to FIG. 20B, another embodiment of an assembly of lightemitting devices 904 is shown in cross-sectional schematic. In thisembodiment, first and second wavelength-converting layers 578 a and 578b, respectively, are disposed on different dielectric layers overlyingthe LEDs. First wavelength-converting layer 578 a is disposed on adielectric layer 940 and second wavelength-converting layer 578 b isdisposed on a dielectric layer 950. In this manner, eachwavelength-converting layer may be fabricated and partitioned fromdifferent wavelength-converting layers. In other embodiments, there maybe even more dielectric and wavelength-converting layers than shown inFIG. 20B. Any suitable light emitting device, such as those described inFIGS. 5-8, may be used in the assembly.

What is claimed is:
 1. A method for forming a light emitting device, the method comprising: providing a transistor substrate having a top surface and a bottom surface, the top surface comprising a plurality of conductive regions; forming two transistors in the top surface of the transistor substrate and a capacitor; providing an LED substrate; forming an LED on the LED substrate, the LED having a largest area and wherein the LED comprises gallium nitride, indium gallium nitride, indium arsenide, aluminum gallium arsenide, gallium arsenide, gallium phosphide, gallium arsenide phosphide, aluminum indium gallium phosphide, gallium arsenide nitride, aluminum indium arsenide, aluminum antimonide, indium phosphide, indium antimonide, or indium gallium arsenide phosphide, and combinations thereof; forming a reflector layer; bonding the two transistors, capacitor, and transistor substrate to the LED, wherein after bonding, the reflector layer is disposed between the LED and the transistor substrate, the LED is in operative communication with at least one of the two transistors, and the LED overlies the two transistors and capacitor; removing a portion of the transistor substrate; and forming a plurality of through substrate interconnects, wherein each through substrate interconnect of the plurality extends through the transistor substrate from the conductive region of the plurality of conductive regions to the bottom surface of the transistor substrate.
 2. The method of claim 1, wherein the capacitor is a stack capacitor disposed between either the first transistor or the second transistor and the LED.
 3. The method of claim 1, wherein the capacitor is a trench capacitor wherein at least a portion of the trench capacitor is disposed between the top surface and the bottom surface of the transistor substrate.
 4. The method of claim 1, wherein the transistor substrate comprises single crystal silicon.
 5. The method of claim 1, wherein the transistor substrate comprises an etch-stop layer.
 6. The method of claim 1, wherein after the step of removing a portion of the transistor substrate step, the transistor substrate has a thickness less than 20 microns.
 7. The method of claim 1, wherein the reflector layer comprises a distributed Bragg reflector.
 8. The method of claim 1, further comprising providing a backboard, wherein the backboard comprises an interposer, wherein the interposer comprises a plurality of backboard interconnects.
 9. The method of claim 8, further comprising bonding each through substrate interconnect of the plurality of through substrate interconnects to a backboard interconnect of the plurality of backboard interconnects.
 10. The method of claim 9, further comprising removing the LED substrate.
 11. The method of claim 1, further comprising providing a wavelength-converting layer, wherein the wavelength-converting layer overlies the LED.
 12. The method of claim 1, wherein the largest area of the LED is 2,500 square microns or less.
 13. The method of claim 1, wherein the largest area of the LED is 100 square microns or less. 